As a catalyst used for producing olefin polymers such as homopolymers or copolymers of ethylene and/or α-olefins, catalysts containing a titanium compound loaded on activated magnesium halide have been known so far. As such olefin polymerization catalysts (hereinafter, “polymerization catalysts” may include copolymerization catalysts), there are known catalysts containing a solid titanium catalyst component composed of magnesium, titanium, halogen, and an electron donor and an organoaluminum compound.
These catalysts have high catalytic activity for polymerization of C3 or higher α-olefins such as propylene and 1-butene and copolymerization of two or more monomers selected from such α-olefins, similarly to the case of ethylene polymerization. Further, the resulting copolymers have high melting points because of high tacticity and crystallinity. It is known that, among these catalysts, a catalyst containing a solid titanium catalyst component loading an electron donor selected from carboxylates including phthalates as typical examples, an alkylaluminum, and a silicon compound having at least one Si—OR (wherein R is a hydrocarbon group) serving as cocatalysts exhibits particularly excellent performances (for example, Japanese Patent Laid-Open Publication No. S57-63310, Japanese Patent Laid-Open Publication No. S58-83006, etc.).
It is also disclosed that a catalyst containing a solid titanium catalyst component containing a compound with two or more ether linkages as an electron donor has high polymerization activity (for example, Japanese Patent Laid-Open Publication No. H3-706, Japanese Patent No. 3476793, Japanese Patent Laid-Open Publication No. H4-218508, Japanese Patent Laid-Open Publication No. 2003-105022, etc.).